Degradation and removal mechanisms of mixed veterinary antibiotics in swine manure during anaerobic and storage treatments: Validation and characterization

The presence of mixed veterinary antibiotics (MVAs) in swine farms raises environmental concerns, necessitating a thorough examination of its degradation and removal mechanisms. In this study, a series of batch experiments were conducted to explore the degradation, biodegradation, and adsorption of mixed tetracycline (TC), oxytetracycline (OTC), norfloxacin (Norf), and sulfadiazine (SDZ) under anaerobic and storage swine manure treatments. Results revealed a varied antibiotics removal pathway despite their mixture, with dominant degradation mechanism for TC, biodegradation for OTC and SDZ, and adsorption for Norf. Anaerobic conditions exhibited higher MVAs removal (average of 44.65 +/- 14.9 %) compared to storage conditions (average of 36.22 +/- 11.2 %). MVAs' removal pathways showed different significant responses to contact time, temperature, and initial concentration. On the other hand, Degradation half-lives of MVAs were prolonged, particularly for TC and Norf, in contrast to OTC and SDZ. These half-lives were overall shorter under anaerobic conditions than in storage conditions. Storage condition was favourable for MVAs adsorption onto swine sludge than anaerobic condition. Furthermore, MVAs adsorption behaviour into modified bentonite (MB) showed a high capacity except for SDZ, higher adsorption under storage conditions compared to anaerobic conditions. MVAs' adsorption onto MB fitted well with the pseudo-second kinetic model. The outcomes of this research would provide a more in-depth understanding of MVAs removal mechanisms during the anaerobic and storage treatments of animal wastes.